Riley stated that the minimum speech sample length necessary to compute his stuttering severity estimates was 200 syllables. This was investigated. Procedures supplied for the assessment of readers and non-readers were examined to see whether they give equivalent scores. Recordings of spontaneous speech samples from 23 young children (aged between 2 years 8 months and 6 years 3 months) and 31 older children (aged between 10 years 0 months and 14 years 7 months) were made. Riley’s severity estimates were scored on extracts of different lengths. The older children provided spontaneous and read samples, which were scored for severity according to reader and non-reader procedures. Analysis of variance supported the use of 200-syllable-long samples as the minimum necessary for obtaining severity scores. There was no significant difference in SSI-3 scores for the older children when the reader and non-reader procedures were used. Samples that are 200-syllables long are the minimum that is appropriate for obtaining stable Riley’s severity scores. The procedural variants provide similar severity scores.